Dysregulation of autoreactive B cells has been implicated in systemic lupus erythematosus (SLE). Disease occurs when B cell tolerance is overcome and cells specific for nuclear antigens renew signal transduction through the BCR leading to autoantibody secretion. Understanding the mechanisms that induce and maintain an unresponsive state in B cells is crucial to understanding the molecular basis of SLE. In this application we will test the hypothesis that tolerance to Sm is overcome when antigenic epitopes are displayed on the membrane blebs of apoptotic cells. We propose that this unique display of highly ordered membrane-bound epitopes overcomes a state of partial anergy in anti-Sm B cells by renewing signal transduction through the BCR. Sm-specific B cells (2-12/Vk8 Dbl) develop into mature B2 cells that exhibit an activated cell surface phenotype and fail to secrete anti-Sm antibodies in response to LPS. Interestingly, other phenotypic changes associated with anergic B cells are absent in the 2-12Nk8 Dbl B cells suggesting a state of partial anergy. In aims 1 and 2a, we will assess if the partially anergic phenotype is associated with incomplete desensitization of the BCR and if antigens displaying higher valency epitopes, such as spliceosomes, tetramers of Sm, or apoptotic membranes, are capable of renewing signal transduction. Mechanistically, renewed signal transduction may occur when desensitized receptors repartition to membrane microdomains called lipid rafts. In aim 2b we will assess if the BCR on 2-12/Vk8 Dbl B cells are excluded from lipid rafts and if these receptors are capable of translocating to the rafts upon ligation by high valency antigens. In aim 3 we will assess the effect of apoptotic cells on tolerance to Sm using an in vivo model. First, we will inject apoptotic cells into the 2-12/Vk8 Dbl mice and assess if tolerance to Sm can be overcome. In a second approach, we will introduce a defective mer gene into the 2-12/Vk8 Dbl immunoglobulin transgenic model and assess if increased levels of apoptotic cells overcome tolerance by inducing Sm-specific autoantibodies.